1. Field of the Invention
The present invention relates generally to improved methods of reducing proppant flowback and the production of formation fines in fluids produced from subterranean formations, and more particularly, to introducing shape memory sieves into hydraulic fractures in the subterranean formation to strain proppant and formation fines from produced fluids.
2. Description of the Prior Art
The entrainment of particulate matter in fluids produced from subterranean formations is a significant problem. Entrained particulate matter may precipitate, causing problems like clogging small orifices in valves and other devices, and eroding pipeline components. The erosion problem is particularly severe in high-pressure, high-flow rate situations, for example, where producing natural gas or oil.
Some of this problematic particulate matter is formation fines, but another significant source can be solid particulate material introduced into the well during hydraulic fracturing treatments. Hydraulic fracturing techniques, intended to enhance production by forming and propping open fractures in subterranean zones, are well known to those skilled in the art. Typical hydraulic fracturing processes involve pumping at high pressure a viscous fracturing fluid through the wellbore and into the subterranean formation, thereby creating fractures in the formation. These fractures are intended to allow the desired fluids in the formation to flow more readily into the wellbore. When the pressure of the fracturing fluid is relieved, the fractures will tend to close. Thus, fracturing fluids usually contain suspended solid particulate material, intended to be deposited within the fractures to prop the fractures open once the pressure of the fracturing fluid is relieved. This suspended solid particulate material is referred to in the art as xe2x80x9cproppant.xe2x80x9d Proppant may be sand or ceramic beads of suitable mesh size. Once the fracturing fluid has created fractures in the formation and flowed into those fractures, the proppant is precipitated out of the fluid by reducing the viscosity of the fluid using techniques known in the art. The deposited proppant prevents the fractures from completely closing when the pressure of the fracturing fluid is relieved.
The distribution of the proppant in the fractures creates a permeable medium through which the desired fluids will flow from the formation to the wellbore. Commonly, this distribution is uneven, resulting in channels of varying size in the proppant bed, and in a quantity of the proppant not being trapped in the fractures. If the channels in the trapped proppant bed are of sufficient size, the fluids flowing through the channels will entrain loose proppant and carry it to the wellbore. This undesirable occurrence is referred to as xe2x80x9cproppant flowback.xe2x80x9d Proppant flowback can cause problems like clogging and eroding of pipeline components.
Many methods are known in the art for reducing proppant flowback and the production of formation fines. For instance, gravel packs and screens may be placed at the entrance to the wellbore. While gravel packs may prevent the production of particulate matter with formation fluids, they often fail and require replacement due to, inter alia, the deterioration of the perforated or slotted liner or screen as a result of corrosion or the like. Additionally, gravel packs are expensive to install, and the removal and replacement of a failed gravel pack is even more expensive.
Methods for retaining proppant within the fractures to prevent flowback also are known. For example, proppant material can be coated with curable resins that cause the proppant to agglomerate and consolidate within the fractures, thus reducing the amount of flow-back. However, these resins are expensive and may not withstand the effect of stress cycling during production and shut-in of the well. Other known methods such as mixing fibers or deformable particulate matter with the proppant also are not satisfactory.
Thus, there is a continuing need for improved methods of reducing proppant flowback and production of formation fines when producing fluids from subterranean formations that will overcome the limitations of known methods.
The present invention provides improved methods for reducing proppant flowback and the production of formation fines from hydraulic fractures in subterranean formations. More particularly, the present invention involves introducing compressed shape memory sieves into the fractures and then inducing the compressed sieves to return to their original shape, thereby forming permeable barriers within the fractures that prevent proppant and formation fines from being entrained in the produced fluids.
In one embodiment of the present invention, compressed sieves made from a shape memory material are carried into hydraulic fractures by the fracturing fluid during hydraulic fracturing operations. When the heat of the surrounding formation raises the temperature of the sieves sufficiently, the sieves substantially return to their pre-compression size and configuration. The sieves thereby wedge themselves into place within the fracture and filter fluids flowing from the formation to the wellbore.
In another embodiment of the present invention, compressed sieves made from a shape memory material are introduced into hydraulic fractures subsequent to the hydraulic fracturing operation. This requires injecting a fluid carrying the sieves through existing well casing perforations, preferably using pinpoint injection techniques.
Other and further objects, features, and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments that follow.